Under The Erzhus
Erzhu Rong was impressed with Gao Huan's talents, and he made Gao one of his military commanders. In 528, Emperor Xiaoming, displeased at the hold on power that Empress Dowager Hu's lover Zheng Yan (鄭儼) and Zheng's associate Xu Ge (徐紇) had, entered into a conspiracy with Erzhu to have Erzhu advance on the capital to force Empress Dowager Hu to kill Zheng and Xu. Erzhu therefore began to march on the capital, and he made Gao his forward commander. On the way, however, Emperor Xiaoming ordered him to stop, but the news of the conspiracy still leaked, and Empress Dowager Hu poisoned Emperor Xiaoming to death and declared his distant toddler nephew Yuan Zhao emperor.
Erzhu refused to recognize Yuan Zhao as emperor, and he continued his march on Luoyang, declaring Yuan Ziyou the Prince of Changle emperor (as Emperor Xiaozhuang). Luoyang's defenses collapsed, and Erzhu arrested and threw Empress Dowager Hu and Yuan Zhao into the Yellow River to drown. Believing that the imperial officials would never obey him, he massacred a large number of them (including Emperor Xiaozhuang's brothers), and Emperor Xiaozhuang, fearing what would come next, offered to yield the throne to Erzhu. Gao suggested that Erzhu accept the offer, but Erzhu hesitated and ultimatedly ruled against it. His general Heba Yue (賀拔岳), who opposed Erzhu's taking of the throne, suggested Erzhu that Gao should be executed to show his good faith, but Erzhu ruled against it. In fact, for Gao's contributions to the campaign, Emperor Xiaozhuang created him the Count of Tongdi.
Erzhu subsequently carried out a number of campaigns against agrarian rebels to try to reunify the empire. Gao thereafter participated in the campaigns against Ge Rong and Xing Gao (邢杲), as well as the rebel general Yang Kan (羊侃), serving with distinction. On one occasion, when Erzhu Rong was asking his commanders for opinions on who could succeed him as the commanding general of the army if he were no longer there, most commanders opined that Erzhu Zhao could, but Erzhu Rong himself opined that Gao Huan was the only one capable of doing so, and he warned Erzhu Zhao, "You are no match for Gao Huan, and one day he will surely pierce through your nose." Erzhu Rong thereafter made Gao the governor of Jin Province (晉州, roughly modern Linfen, Shanxi), and while governor, Gao gathered much wealth, intending for use later.
In 530, Emperor Xiaozhuang, believing that Erzhu would eventually seize the throne, ambushed and killed him in the palace. The Erzhus, led by Erzhu Zhao and Erzhu Rong's cousin Erzhu Shilong, fought against Emperor Xiaozhuang, and Erzhu Zhao was thereafter marching on Luoyang, declaring Erzhu Rong's wife the Princess Beixiang's nephew Yuan Ye emperor. Erzhu Zhao summoned Gao to aid him, but Gao declined, using the excuse that he needed to fight against local agrarian rebels. Erzhu Zhao was displeased, but for the time being did not act against Gao. Later in the year, Erzhu Zhao captured Luoyang and arrested Emperor Xiaozhuang, delivering Emperor Xiaozhuang to his headquarters at Jinyang (晉陽, in modern Taiyuan, Shanxi). Gao wrote a letter to Erzhu Zhao urging him not to harm the emperor, but Erzhu Zhao refused to answer, and subsequently strangled Emperor Xiaozhuang to death.
Despite this, Gao remained nominally under the Erzhus' command structure, and when, around the new year, the general Gedouling Bufan (紇豆陵步番), loyal to Emperor Xiaozhuang, attacked Erzhu Zhao and initially defeated him, approaching Jinyang, Gao came to Erzhu Zhao's aid, and together they defeated and killed Gedouling. After the battle, Erzhu Zhao and Gao swore themselves to be brothers. Erzhu Zhao, trusting Gao, commissioned him with Ge Rong's former troops (largely Xianbei) and, accepting his suggestion, allowed him to take his new troops east of the Taihang Mountains to seek food.
In spring 531, Gao Huan was posturing to attack his distant relative Gao Gan (高乾), who had declared a rebellion at Xindu (信都, in modern Hengshui, Hebei), against the Erzhus. However, Gao Gan and Li Yuanzhong (李元忠) were able to persuade him that the Erzhus, because of their corruption, were hated by the people, and he could overthrow them. Gao Huan thereafter stirred his troops by forging orders from Erzhu Zhao that indicated that Erzhu Zhao was about to turn them into servants for his own troops. Gao Huan's troops believed the forged orders, and when he declared a rebellion in summer 531, they supported him.
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